Synthetic rubber and preparation thereof



nium soaps, it may be desirable to have a slight weight of polymerization monomers. In place of,

Patented July 20, 1954 2,684,356

SYNTHETIC RUBBER AND PREPARATION THEREOF Ervlng Arundale and Fred W. Banes, Westfield, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application July 3, 1950, Serial No. 172,007

6 Claims. (01. 26080.7)

emulsifier such as the sodium salt of a formaldehydo condensed naphthalene sulfonic acid, or sodium lauryl sulfate, sodium tetraisobutylene sulfonate or aromatic alkyl sulfonate salts, etc. may be used also.

The polymerization may be carried out at temperatures between about 20 C. to +60 C., but diene, and 25% by weight of acrylonitrile, moditemperatures between 30 and 50 C. are most fied during polymerization by .05% by weight of common. When the polymerization temperature divinylbenzene. 10 is below the natural freezing point of the emul- The diolefin which may be used may include sion, as in the so-called Redox systems described butadiene-1,3, isoprene, piperylene, dimethyl buin Industrial and Engineerin Chemistry, vol. 40, tadiene, Z-methyl pentadiene, etc. or mixtures pp. 770-777 and pp. 932-937, it is necessary to thereof, add an anti-freeze agent such as methanol, eth- The nitrile comonomer should be a compound anol, ethylene glycol or glycerine. The polymerihaving the general formula CH2=C(R-) CN zation reaction may be carried to a conversion of where R is hydrogen, methyl, ethyl or chlorine. about 50 to 100%, preferably 65 to 85%, and nor- The cross-linking agent to be used is prefermally requires between about 5 and 48 hours deably a divinyl aromatic hydrocarbon, such as dipending on the temperature and other factors, as vinyl benzene, divinyl toluene, divinyl xylene, diis well-known.

Vinyl naphthalene, di-isopropenyl benzene, etc. The catalyst used may be any one or a mixture having the two vinyl groups in any of the ortho, of the known class of oxygen-liberating catalysts meta, or para positions; but in place of such such as hydrogen peroxide, benzoyl peroxide, compounds, one may use other organic comcumene hydroperoxide, tertiary butyl hydroperpounds having two reactive cross-linking groups, oxide, potassium persulfate or other alkali metal such as various dimercaptans, e. g. decamethylene persulfates or perborates or the corresponding mercaptan, dithiophenol, bis mercapto methyl ammonium salts. Between 0.05 to 2% of catalyst 1 1, t based on weight of monomers is used, the opti- The proportions in which the above three remum amount being dependent primarily on cataactants are used may vary somewhat accord- 3O lyst type and polymerization temperature. ing to the purposes for which the synthetic rub- Furthermore, about 0.25 to 1.0% of a mercapher is to be used, but normally will be within the tan modifier based on weight of monomers is also limit of 55-85, preferably 65-82, per cent by rm ly p n h m rc ptans may be priweight of diolefin, 15-45, preferably 18-35, per mary or tertiary mercaptans having 6 to 18 car cent by Weight of the nitrile monomer, and .01 on atoms such as hexyl, decyl, dodecyl, tetra- 1.0, preferably 0.05-0.5, per cent by weight of the decyl, or ootadecyl, but preferably a mixture comcross-linking agent. prising a substantial percentage of dodecyl with The preferred method of carrying out the polyminor amounts of other C10 to C14, mercaptans. merization is to emulsify the reactants in water, In the emulsification, the amount of water to with a suitable emulsifier, together with a suitbe used should be about 0.5 to 3.0, preferably 1 able catalyst, and preferably with the addition to 2, volumes per volume of mixed reactants. of one or more of the known polymerization mode reactio t me Should generally be about 1 to ifiers, and maintaining the resultant emulsion at 50 h preferably 5 to 30 sthe desired polymerization temperature until the Thus, according to the present invention, the desired degree of polymerization has been atuse of a controlled small amount of cross-linking rai d, agent effects improvements in the diene-nitrile Suitable emulsifying agent include the various synthetic rubber both in the latex form and in water-soluble soaps such as alkali metal soaps, the y rubber form- The use of divinyl benzene e. g. sodium stearate, sodium oleate, or other or other cross-linking agent mentioned, improves sodium, potassium and ammonium soaps of satthe wet gel strength of the d m i latoX, urated or slightly unsaturated fatty acids of 8 to nd, afte coa u at on, the dry rubber has sub- 24, preferably about 12 to 20 carbon atoms, such stantially improved prooessa ty d other as stearic, oleic, caprylic, palmitic, lauric, carnau- Characteristics, h as reduced banding t me big, etc, acids, Sodium or potassium soaps of and reduced calender shrinkage. Another suroleic or stearic acid are usually preferred, and p g result is t t t e present t on oboften a slight excess of fatty acid over alkali may tains improved pr cessability although the Wilbe beneficially present. In the case of ammoliams plasticity value is increased, and the molecular weight is increased.

The invention will be better understood from This invention relates to a new type of oil-resistant rubber, and the preparation thereof. More particularly, it relates to a diene-nitrile type of synthetic rubber modified by a certain controlled small amount of particular cross-link- 5 ing agents. The invention may be illustrated by a copolymer of about by weight of butaexcess of ammonia. The amount of emulsifier,

such as the above mentioned soaps, should be the following experimental data:

about 0.5 to 5 parts by weight per parts by 0 A series of five runs were made using various amounts of divinyl benzene ranging from 0 to or in addition to, the ordinary soaps another 0.50% by weight (on the weight of reactants),

using a diene-nitrile monomer mixture consisting of 74% by weight of butadiene and 26% by initially, FA, at 20% conv., at 50% conv.

weight of acrylonitrile. The following general Reaction conditions 8-9 hours conditions were used in carrying out this series at 31 C. to of polymerizations: 5 75% con- Ratio water/reactants 1.8/1. Vermon- Per cent oleic acid (on reactants) 3.25. The samples taken during t runs at com Extent of neutralization version levels of approximately 20, 35, 50, 65 and Per cent K2S2O8 (on reactantSL-n were stabilized, coagulated, washed, dried Per cent mercaptan (on reactantsn and analyzed for gel content and molecular Divinyl benzene Variedweight. The polymer possessing the highest Polymerized 17 at molecular weight (400,000) and a low gel content can be obtained using 0.05% divinyl ben- The lattices were short-stopped with 0.2% r zene and carrying the polymerization to -70% hydroquinone, stabilized with 2% phenyl beta conversion. naphthyl amine and then coagulated, and the The latices from the three runs containing polymer washed and dried. 0, 0.05, and 0.25 part of divinyl benzene were The resulting polymers showed the following short-stopped at 75% conversion with 0.2% hyevaluation: droquinone and 0.2% 2,6-ditertiary butyl para (Soluble Frac.) Bun Percent Percent Gel Con- Gel Williams IJV B 1 Conv. tent Swell Int M01. Plasticity Visc. Wt.

.05 71 4 5 205 1.53 325,000 121-13 .10 17 3 135 1.27 240,000 137-27 .25 50 s 45 0. 74 105,000 14am .50 74 75 s 25 147-3 1 Percent divinyi benzene on diene-nitrile reactants.

1 Percent conversion after 17 hours at 30-51 0.

The addition of divinyl benzene therefore acticresoi and then vacuum stripped. The stripped vates the synthesis somewhat and as little as latices were creamed to 54% solids using a recipe 0.05 part per 100 parts reactants produces an 35 similar to that used in Example 2 of Patent approximate doubling of the molecular weight 2,444,801, and wet gel strength determinations without causing appreciable gel formation. were run on the concentrates. The data are Larger amounts produce extensive cross-linking given below: with a resulting high gel content, and the'plasticity also increases when increasing the quan- 40 I 1 Gel tity 0f DVB' Fercent Divin lBenzene Vn Lem,

Another series of runs was made to show the y mas/my corresponding improvement in wet gel strength of a diene-nitrile rubber latex, using a small 331 amount of divinyl benzene as cross-linking imgg-i prover. 7 1310 Three turbomixer runs were made under the standard conditions listed below. Samples were removed at various intervals so that changes in gel content, gel swell, and molecular weight could be followed throughout the runs.

Ratio butadiene/acrylonitrile 4/20. Ratio water/reactants 1.8/1. Per cent oleic acid (on reactants) 3.25.

Extent of acid neutralization Per cent KZSZOB (on reactants) 0.3.

Per cent rnorpholine (on react- 0.1.

ants).

Per cent divinyl benzene Va 'ied Per cent lorol mercaptan (on re- 0.53.

actants) (Mercaptan added /2 It appears that the wet gel strength of substantially gel free polymers can be improved through the addition of small amounts of divinyl benzene. However, the improvement obtained can be attributed to the increase in polymer plasticity which occurs as a result of the addition of the cross-linking agent.

The same three latices, together with an additional one made using 0.50% divinyl benzene in the polymerization, were coagulated with brine and carbon dioxide and the polymers washed and dried 8 hours at 170 F. The properties of the polymers and the evaluation data are presented in the following table:

Milling, Min. lgereeut Vulc. 60 at 287 F.

011- gg g ggg? Gel Plast. B d B1 k ee;

an so i "in age (a) (b) (c) Tens. Mod. Eiong.

Formula: Polymer 100, zinc oxide 5, stearic acid 1, MP0 Black 50, sulfur 1.5, A1-

X .1. (11) Minutes required to band 300 g. on a 6" x 12 mil]. (b) Minutes required to incorporate 150 g. of MPO black into 300 g. of polymer on a 6 X 12 mill (0) A test compound of parts of polymer and 50 parts of MP0 black was used for this test.

zone, the tensile strength,

For a given amount of mercaptan modifier therefore, an increase in th amount of divinyl benzene added produces an improvement proessability, a reduction in calender shrinkage, increase in tensile strength modulus, and a reduced elongation. This improvement in ros-- essing characteristics is interesting in View the fact that the gel content of the polymer and the Williams plasticity increase with increased amounts of cross-linking agent. iieretofore, it has been found that polymer processabil improved as the Williams plasticity is decrease Calender shrinkage is important where ca endered sheet formed should kee the imprint of the original shape. The rubber shoe industry is one example Where shrinkage must be quite small in order to keep the pattern clear and definite. Other uses where calender shrinkage must be low are soles of shoes, rubbers, cover belts, etc. A shrinkage of is considered good and less than 5% is excellent.

It is herewith intended to claim all modifications coming within the scope spirit of the invention.

What is claimed is:

l. A synthetic rubber copolymer about -85% by weight of butadiene and 15-15% weight of acrylonitrile, and also ha 'fillg copolymerized therewith .05 to 1.0% by weight of divinylbenzene, said copolynier being adapted, upon curing, to have less calender sh kage and greater tensile strength than a copolyrner similar except without the cross-linking agent.

2. An oil-resistant synthetic rubber copolymer of -7 i% by Weight of butadiene, 26435 of acrylonitrile, and .05-0.5% of divinyl said copolymer having not over gel, a Williams plasticity of about 114465, said copolynier being adapted, upon curing, to have less calender shrinkage and greater tensile strength than a copolymer similar except without the divinyl be. after 60 minute cure, being at least 2200, and the 300% modulus being at least 1475.

3. An oil-resistant synthetic rubber copolymer of about 74% by weight of butadiene, 26% of acrylonitrile and about 0.25% of divinyl benzene, said copolyzner having a Williams plasticity of about 165, a banding time of about 3 minutes to band 300 grams on a 6 x 12" rnill, a calender shrinkage of about 22.1% and, after a 60 minute cure, a tensile strength of about 3315 pounds per sq. inch and a 300% modulus of about 2435, said tensile strength and modulus being substantially higher than obtainable with a similar copolymer free from divinyl benzene.

i. The process which comprises subjecting to emulsion polymerization a monomer mixture 55--85% by weight of butadiene, 15-45% by weight of acryloi trile and .05 to 1.0% by weight oi diviuylbenzene with 3.5 to 3 volumes oi water per volume of mixed reactants, in the presence or a peroxidizing type polymerization catalyst, at a temperature between 2c C. and +50 whereby an oil-resistant synthetic rubber copolymer is produced which adapted, upon curing, to have less calcndei rage and greater tensile st engt'n than similar copclymer free from ClOSS-lilliI 5. The process 0 comprising sparing an improved oilresistan synthetic -1' comprising subjecting to emulsion polymeric on a monomer mixture consisting essentially oi 5 74% by Weight of butadiene, 26-35% by w of acryionitrile, and .05 to 0.5 by weight of uivinyl benzene, with about i. 2 volumes of water per volume of mixed reactants, in the presence of 0.5 to 5.0% by Weight of emulsifying agent, based on the weight of reactants, and in the presence of 0.25 to 1.0% of a polymerization modifier comprising an alkyl inercaptan or" 0 to carbon atoms, and in the presence of a percxidizing polymerization catalyst, at a temperature of about l0 to 45 C. for a reaction time of about 530 hours, whereby there is produced a copolymer having not over 75% gel, a Williams plasticity of about 114465, and adapted, upon to have less calender shrinkage greater tensile strength than a similar copolyrner tree iron divinyl benzene.

6. The process preparing an improved oilresistant synthetic rubber which consists essentially in subjecting to emulsion polymerization a monomer mixture consisting essentially of 74% by weight of butadiene, 26 of acrylonitrile and about of divinyi benzene, with about 1 to 2 volumes or water per volume of mixed reactants, in the presence of 0.5 to 5.0% by weight of emulsifyin agent, based on the weight of reactants, and in the presence of about 0.53 to 0.80% of a polymerisation modifier consisting essentially of alkyl mercaptans of 10 to 14 carbon atoms, and in the presence or" a peroxiclizing type polymerization catalyst for about 17 hours at about 30-31 0., whereby there is produced a product as described in claim 3.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,281,613 Walthan et a1. May 5, 19-12 2,47%,80? Schoene July 5, 1949 OTHER REFERENCES Schoene et al.: Ind. and Eng. Chem, Vol. 38; No. 12, December 1946, pages 1246-1249. 

1. A SYNTHETIC RUBBER COPOLYMER OF ABOUT 55-85% BY WEIGHT OF BUTADIENE AND 15-45% BY WEIGHT OF ACRYLONITRILE, AND ALSO HAVING COPOLYMERIZED WHEREWITH .05 TO 1.0% BY WEIGHT OF DIVINYLBENZENE, SAID COPOLYMER BEING ADAPTED, UPON CURING, TO HAVE LESS CALENDER SHRINKAGE AND GREATER TENSILE STRENGTH THAN A COPOLYMER SIMILAR EXCEPT WITHOUT THE CROSS-LINKING AGENT. 